I. Field
The present invention relates generally to data communication, and more specifically to multi-antenna transmission for spatial division multiple access (SDMA) in a multiple-input multiple-output (MIMO) communication system.
II. Background
A MIMO system employs multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas may be decomposed into NS spatial channels, where NS≦min{NT, NR}. The NS spatial channels may be used to transmit NS independent data streams to achieve greater overall throughput.
In a multiple-access MIMO system, an access point can communicate with one or more user terminals at any given moment. If the access point communicates with a single user terminal, then the NT transmit antennas are associated with one transmitting entity (either the access point or the user terminal), and the NR receive antennas are associated with one receiving entity (either the user terminal or the access point). The access point can also communicate with multiple user terminals simultaneously via SDMA. For SDMA, the access point utilizes multiple antennas for data transmission and reception, and each of the user terminals typically utilizes one antenna for data transmission and multiple antennas for data reception.
Some key challenges for SDMA in a multiple-access MIMO system are (1) selecting the proper set of user terminals for simultaneous transmission and (2) transmitting data to and/or from each selected user terminal in a manner to achieve good system performance. There is therefore a need in the art for techniques to efficiently support SDMA for a multiple-access MIMO system.